104 HUMAN PHYSIOLOGY 



magnesium phosphate, ammonium urate, and the phosphates and 

 carbonates of the alkali earths. 



The amount of urine excreted per day is generally about 

 1.5 litres. 



Urine contains about 4$ solids, among which are : 



(a) Nitrogenous wastes of metabolism: urea 2.3$ (35 g. 

 per day), uric acid (0.05$ in the form of acid salts of the 

 alkalies), hippuric acid, kreatinin (0.05$), xanthin, hypo- 

 xanthin, ammonia salts (0.04$). The urea contains 83-86^ 

 of all the nitrogen of the urine. 



To obtain the urea from urine, evaporate the urine to small 

 bulk and add nitric acid ; this throws down crystals of nitrate of 

 urea. 



The uric acid crystallizes from the urine when that is mixed 

 with one-tenth its volume of concentrated hydrochloric acid and 

 left standing in the cold. This separation of the uric acid takes 

 place in concentrated and strongly acid urine without the addition 

 of hydrochloric acid (sedimentum lateritium, see page 46). 



The urea contains 83-86$ of all the nitrogen of the urine ; 

 ammonia contains 3-4$; the remaining nitrogen is distributed 

 among uric acid, kreatinin, etc. 



(b) Salts about 1.5^, chiefly sodium chloride (a little more 

 than if) and, in smaller quantities, phosphates, sulphates, 

 and traces of oxalates; among the bases are sodium, potas- 

 sium, magnesium, calcium, and traces of iron. 



Besides the sulphates, the urine contains sulphuric acid combined 

 with the ethereal sulphates of the benzene derivatives, e.g. : 



Phenyl-sulphuric acid C fl H..O.SO 2 .OH 



Kresyl-sulphuric acid C 7 H 7 .O.SO,.OH 



Indoxyl-sulphuric acid or indican C 8 H 6 X.O SO 2 .OH 



Skatoxyl-sulphuric acid C 9 H 8 N.O.SO,.OH 



To demonstrate the presence of indican, add a like quantity of 

 concentrated hydrochloric acid and a little calcium chloride solu- 

 tion to the urine. Indigo is produced which may be collected by 

 shaking it with chloroform. 



The benzene derivatives, with which the sulphuric acid unites, 

 are derived from the intestine, where they are formed by proteid 

 putrefaction: phenol, indol, skatol; the last two, after being 



